The present invention relates to an anvil pad configuration for use in a laser cleaving process and, more particularly, to a relatively small anvil pad that is designed to not overhang the edges of the wafer or bar during cleaving.
In the manufacture of devices such as semiconductor lasers and amplifiers or superluminant diodes, the initial fabrication steps are performed on a semiconductor wafer containing hundreds of separate devices. After an initial set of processing steps (defined as "wafer level" processing), the wafer is broken into a number of separate rows of devices, where these rows are referred to in the art as "bars". After additional processing of the devices in bar form, it is necessary to break the bar to form the individual optical devices. In conventional optical device processing, the formation of bars and devices is usually performed by a cleaving process. Typically, the cleaving process requires that the wafers or bars be placed on a thin supporting membrane. Tick marks are then placed at the desired locations where the cleave is to be initiated, and a tensile strain is applied to the material to be cleaved in order to initiate crack formation and propagation from the tick mark through the bulk of the material. The tensile strain is generated by a bending moment formed by force and applied to the top and bottom surfaces of the material. One force is generally applied to the side opposite the tick mark using the edge of a "support mandrel" or, alternatively, a knife edge. In the case of the support mandrel, the force applied to the side carrying the tick mark is generated by a pair of rolling wheels that straddle the edge of the support mandrel and press on the material to be cleaved at or near the edges of the final pieces being cleaved. In the case of knife edge breaking, the force applied to the side carrying the tick mark is generated by a flat anvil pad which is slightly compliant so that the pad can accommodate the bending strain that is generated in the material to be cleaved when the pad presses the material against the knife edge. In both of these systems, there is potential for damage and contamination of the top edge of the facet of the device being cleaved due to contact of the cleaving device with the top surface at or near the device's edge.
An exemplary embodiment of the present invention utilizes an anvil pad including a centrally disposed slit, where this slit will align with a top surface scribe mark during cleaving. The slit in the pad allows the generation of a specified applied bending moment with a lower applied force than a non-slit pad. The optimal dimensions of the slit depend on the width, thickness and material being cleaved, and to a lesser extent the radius of curvature of the pressure edge below the device. The lower force required to initiate cleaving is advantageous since the smaller force means there is less elastic energy stored in the material prior to crack formation, and therefore less energy to be dissipated in the device after the cleave process has absorbed the small amount of energy needed to split the crystal planes.
In one form, the anvil of the present invention may comprise a tool steel upper portion and a compliant lower portion, where the compliant portion contacts the device surface. Alternatively, a membrane tape may be disposed between the anvil and the device, with the tape advancing after each cleaving operation so as to carry away any possible debris from one cleave and present a "clean" compliant surface for each subsequent cleave.
Other and further advantages of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.